The invention concerns a measuring and recording system for determination of the distribution and position of media which enclose the device, chiefly in its longitudinal axis. It is based on thermodynamic properties of the media, such as thermal conductivity and capacity.
More specifically, the invention concerns a measuring device arranged for determination of the vertical distribution of one or more media which have a thermal connection with the device and where the positions of the interfaces can be determined on the basis of differences in thermal states and properties, comprising an arrangement of one or more thermal conductor elements which have a common thermal reference element and discrete, chiefly thermally insulated sensor areas which, again, have good thermal contact with the medium, being measured through a common partition wall which affords sufficient physical and thermal separation, as well as means for keeping the reference element at a temperature level different from the medium being measured.
In the process industry, especially in the petrochemical industry, it is necessary to be able to record the distribution, position, and thermodynamic state in a process to be able to monitor and control it. The problem of recording the above essentially consists in the fact that the medium is under high pressure and high temperature and also has a consistency which makes it difficult to record transition zones between the individual fractions. In many cases, deposits and various types of choking are problems which make many known principles unsuitable. In addition, the environment inside and outside the process may frequently be of a highly explosive nature. There are many solutions aimed at the recording of distributions and positions of different media based on acoustic, capacitive, and resistive principles. Various types of specific gravity determination also underlie the recording of layers and transition zones in a complex medium being measured. Owing to the foregoing problem presentation, the noted principles are unsuitable on various grounds for the recording of transition zones in special process types.
There are also various sensor systems based on the difference in the thermal conductivity in liquids. For example, mention may be made of Norwegian Patent No. 133517 where, with the aid of an extended thermocouple, a temperature differential is recorded on the inside of a pipe where the warm side of the element also has a thermal connection to an electric heating element. The temperature differential over a given distance in the longitudinal direction of the pipe and the liquid around it is determinative for the signal level.
Among other systems used for measurement of liquid levels, mention may be made of British Patent Application GB-A 2.134.260, U.S. Pat. No. 2,702,476, U.S. Pat. No. 3,280,627, and German Patent (Offenlegungsschrift) 1.959.041. A feature common to all these patents is that it is not possible to record minor changes in thermal properties with sufficiently high resolution.